Threats by Barclays to cut back on lending to households and businesses because of a demand by the Bank of England that it should reduce risks have been criticised by a former policymaker of the central bank.

Robert Jenkins, a former member of the financial policy committee, set up inside the Bank of England look for ticking timebombs in the financial system, said that taxpayers should be concerned that Barclays "continues to sail close to the wind".

The former FPC member wrote to the Financial Times after the Barclays chief executive, Antony Jenkins, warned a requirement that the bank meet a 3% leverage ratio could force it to restrict lending. Barclays had to submit a plan to the Bank of England's new banking regulator, the Prudential Regulation Authority, by Sunday to outline how it would raise its ratio from 2.5% to 3% – which allows banks to have assets worth 33 times their capital.

Robert Jenkins said that the 2.5% leverage ratio used by Barclays meant the bank borrowed 97.5p for every £1 of risk it took. He said there were many ways that Barclays could achieve the higher leverage ratio – and lower risk profile – by retaining more earnings, raising equity, cutting costs, paying less in bonuses or cutting back on lending.

"Of all the options the last in this list was the one its CEO chose to mention. Was this meant as a threat? Was it hubris, reflex or just plain stupidity?"

"The taxpayer should worry that this systemically important financial institution continues to sale close the wind. Its board should worry that its CEO is happy to do so," wrote Robert Jenkins, who until he left the FPC three months ago was regarded as a tough critic of the banking sector and proponent of higher capital.

Nationwide building society has also been hit by the requirement to raise its leverage ratio from 2.1% to 3%. International rules require banks to hit this target by 2019, although it not immediately apparent what timescale Barclays and Nationwide have been asked to work within.

Sign up for the Guardian Today

Our editors' picks for the day's top news and commentary delivered to your inbox each morning.